This invention relates to a method of forming reinforced glass or glass-ceramic composites, and specifically to the formation of glass or glass-ceramic matrixes reinforced with a plurality of randomly oriented and uniformly distributed short fibers such as chopped fibers and/or whiskers forming an integral part of the composite body. The fibers, although uniformly distributed, are not continuous across the length and width of the body as was typical in the laid-up processes of the prior art.
A fiber-reinforced composite comprises a matrix having reinforcing fibers embedded in and bonded to the matrix. In the past, the composites were formed with reinforcing fibers extending the full length or width of the composite, and articles were produced from such composites by cutting such composites to the desired length and width of the article to be formed and stacking a plurality of such composites on top of one another to provide the necessary height of the desired article, and then hot pressing the layers into a final reinforced article. Such continuous fiber composites, however, were very highly anisotropic in terms of their mechanical properties, due to the orientation of the reinforcing fibers. In addition, it was virtually impossible to produce complex or intricate shaped articles with such continuous fiber reinforced composites. Although a majority of the previous composites utilized organic polymer matrixes, more recently, composites employing glass or glass-ceramic matrices have been receiving special attention, particularly in view of the high temperature environments which such matrices are adapted.
In the past, the techniques available for forming glass matrix composites have limited articles to shapes that can be uniaxially hot pressed from essentially planar arrays of reinforcing fibers, such as can be produced from aligned fiber tapes, woven fabrics, felts and the like. In U.S. Pat. No. 4,412,854, for example, a method of making fiber reinforced glass composite articles of complex shape is disclosed wherein sheets of woven or non-woven fiber reinforcement are impregnated with a layer of thermoplastic binder containing glass powder to form a "prepreg". The dried sheets are then cut into a plurality of preforms corresponding to the predetermined pattern of the article being fabricated and stacked in a mold and warm molded to form an intermediate article. The intermediate article is then hot pressed to form the final fiber reinforced glass matrix article.
U.S. Pat. No. 4,511,663 discloses the formation of a prepreg body formed of a glass slurry and metal coated fibers. The impregnated body is then cut into pieces and stacked in a mold and hot pressed into a fiber reinforced composite article. In a like manner, U.S. Pat. Nos. 4,554,197 and 4,717,589 disclose the formation of prepreg sheets, the stacking of the sheets in proper contour for the particular shape to be formed and the consolidation into a laminated composite preform, and finally the hot pressing of the preform into a finished shape.
U.S. Pat. Nos. 4,541,884 and 4,559,262 relate to methods of producing fiber-reinforced structures comprising particular thermoplastic polymers, wherein a tow or roving of glass fibers is pulled through a bath of a low viscosity thermosettable resin to impregnate the fibers, and then consolidated by pulling the impregnated roving from the melt through a die in a process known as pultrusion. The prepreg may be chopped into pellets or granules and used in conventional fabrication processes such as injection molding common in the plastics industry.
In order to produce fiber-reinforced glass matrix articles of complex shapes, it is advantageous to provide short or chopped fibers randomly dispersed within the glass matrix. U.S. Pat. No. 4,780,432 discloses an injection molding technique for producing a chopped fiber-reinforced glass product. However this method requires a high-pressure, high-temperature molding step requiring expensive equipment and extensive and possibly damaging fiber realignment in the molding process.